1. Field of the Invention
The present invention relates to an optical system controller for a video camera which has, as a part thereof, a lens barrel in which is arranged a movable optical system including a zoom lens, an iris diaphragm, and a focusing lens, and on the outer surface of which is arranged a movable mechanism for focusing adjustment, zooming adjustment, and aperture adjustment.
2. Description of the Prior Art
The video camera permits light rays from a subject to pass through an optical system having lenses and enter an imaging unit, so that the image of a subject is projected onto the image plane of the imaging unit. For the image of a subject to be focused sharply at all times, the video camera is required to have autofocusing and zooming capability. (Zooming is the movement of lenses that continuously changes (within a certain range) the magnification of the image of a subject which is projected onto the image plane.) This object is achieved by providing the lens barrel of the video camera with a built-in movable optical system under adequate control.
Such a movable optical system consists of fore-end lens, zooming lens, iris diaphragm, and focusing lens. The iris diaphragm changes its aperture so as to control the amount of light entering the imaging unit, and the zooming lens and focusing lens move along the optical axis.
The movable optical system in the lens barrel causes the zooming lens and focusing lens to move to their adequate positions and also causes the iris diaphragm to have an adequate aperture. These actions are controlled by the mechanisms for focusing adjustment, zooming adjustment, and aperture adjustment, which are mounted on the outside of the lens barrel. Such mechanisms are actuated by movable rings that encircle the periphery of the lens barrel, as shown in FIG. 9.
FIG. 9 is a schematic diagram showing the entire appearance of a conventional video camera. This video camera consists of a camera body 11 and a lens barrel 12 projecting therefrom. The lens barrel 12 has the focus adjusting mechanism 14, the zoom adjusting mechanism 15, and the diaphragm adjusting mechanism 16, each surrounding the outer surface 13 of the lens barrel 12. These mechanisms are arranged in order from the forward end (with a hood) to the camera body 11. Each of these mechanisms is independently rotatable by manual operation with respect to the lens barrel 12.
For autofocusing control, the above-mentioned mechanisms work in such a way that the focusing lens is adequately positioned in the lens barrel according to the position of the zooming lens in the lens barrel. Before the focusing lens finds an adequate position in the lens barrel, it moves back and forth over a comparatively small distance along the optical axis. (This movement is called wobbling.) The range over which the focusing lens wobbles relates to the depth of focus. On the other hand, the depth of focus varies depending on the aperture of the iris diaphragm. Therefore, the autofocusing control involves not only the position of the focusing lens but also the position of the zooming lens and the aperture of the iris diaphragm. Controlling the focusing lens in relation to the zooming lens and iris diaphragm needs information about the position of the focusing lens, the position of the zooming lens, and the opening of the iris diaphragm.
Moreover, zooming requires the focusing lens to follow the zooming lens as it changes the magnification of the image of a subject being projected onto the image plane.
The focusing lens, zooming lens, and iris diaphragm are moved relative to one another by individual motors under programmed control. The amount their movement is usually determined by an electronic control system. In this case, the motors and their circuits and parts may be arranged inside or outside the lens barrel. The motors receive control signals from the movable mechanisms for adjustment of zooming, focusing, and aperture in response to their movement.
The disadvantage of the electronic control system is that the position of the focusing lens and zooming lens and the opening of the iris diaphragm do not correspond directly to the amount of rotation of the movable mechanisms for adjustment of the focusing lens, zooming lens, and iris diaphragm. In other words, the positions of the movable mechanisms do not always indicate the controlled positions of the focusing and zooming lens and the opening of the iris diaphragm.
To cope with this situation, the video camera with the movable optical system and electronic control system is so designed as to display in the view finder or monitor information signals indicating the current positions of the focusing and zooming lens and the current opening of the iris diaphragm. FIG. 10 is a diagram illustrating the view finder or monitor of the conventional video camera which displays information about the positions of the focusing and zooming lens and the opening of the iris diaphragm. In FIG. 10, the image of the view finder or monitor has a meter (17) to indicate the position of the zooming lens, a meter (18) to indicate the position of the focusing lens, and a sign (19) to indicate the opening of the iris diaphragm.
The above-mentioned video camera provided with a view finder or monitor which displays information about the positions of the zooming and focusing lenses and the opening of the iris diaphragm permits the user to know the positions of the zooming and focusing lenses and the opening of the iris diaphragm by watching the view finder or monitor. In other words, the user of the video camera can constantly know the positions of the zooming and focusing lenses and the opening of the iris diaphragm during his camera operation.
In practice, however, the user of the video camera often leaves his eye from the view finder or monitor during his camera operation, because the user tires of continuously watching the view finder or monitor for a long time and the user sometimes needs to see his surrounding scene. This is easily understood from the user's own experience or from the observation of the user's action.
However, once the user of the video camera turns his eye away from the view finder or monitor, he cannot know any longer the positions of the focusing and zooming lenses and the opening of the iris diaphragm in the lens barrel. In other words, the user of the video camera cannot know instantly the positions of the focusing and zooming lenses and the opening of the iris diaphragm while he is waiting for the chance of taking pictures, with his eye turned away from the view finder or monitor. As the result, it is difficult for him to set up immediately the adequate positions of the focusing and zooming lenses and the adequate opening of the iris diaphragm in the case of decisive moment for photographing while he is waiting for a chance. Thus, he would miss the chance to take sharp images at the decisive moment. This situation is serious if the user of the video camera is a professional camera man.
Also, it is not unusual for a professional camera man to take pictures without watching the view finder or monitor; however, in such a case, too, he cannot know the positions of the focusing and zooming lenses and the opening of the iris diaphragm.
The present invention was completed in view of the foregoing. It is an object of the present invention to provide an optical system controller for a video camera having therein an electronically-controlled movable optical system including a zooming lens, focusing lens, and iris diaphragm and also having a lens barrel around which are arranged movable mechanisms for focusing control, zooming control, and aperture control, said optical system controller permitting the user of the video camera to recognize accurately and rapidly the positions of the zooming lens and focusing lens and the opening of the iris diaphragm in the lens barrel while he is not watching the view finder or monitor of the video camera.